1. Field of the Invention
The present invention relates to a system for continuous vacuum forming of a shaped polymeric article and more particularly to vacuum forming a plasticized material on a flexible patterned belt or a pair of rotating belts having apertures therein while providing cooling on both a top surface and a bottom surface of the polymeric material during the shaping process.
2. Description of Related Art
Continuous vacuum forming processes are known for shaping an extruded plastic sheet. U.S. Pat. No. 5,314,325 describes an apparatus for continuous vacuum forming in which hot plasticized material is drawn in contact with a flexibly resilient belt. A cooling station is included for lowering the temperature of the hot plasticized material for final forming while the formed material is still in contact with the flexibly resilient belt. The cooling station includes a water spray means and a water collection means. The water spray means sprays water on a top surface of the formed product for facilitating removal of the final formed product from the belt.
U.S. Pat. No. 6,319,456 describes a method for continuous vacuum forming in which a sheet of hot polymeric material is disposed on a rotating belt having a mold impression. Vacuum pressure is applied to the polymeric material through the belt to draw the polymeric material into contact with the mold impression. The central patterned portion of the sheet is cooled below its heat deflection temperature while leaving at least one lateral edge at a temperature above the heat deflection temperature. The lateral edges are not vacuum formed. The lateral edge is deformed by mechanical deformation while the plastic portion of the lateral edge is still hot. Thereafter, the lateral edge is cooled to a temperature below the heat deflection temperature. A water spray is used for cooling the materials below the heat deflection temperature.
The above described patents have the limitation of only providing cooling on a top surface or a portion of the top surface of a formed article which can result in the formed article not being flat since the bottom surface of the article which does not have cooling can continue to shrink in relation to the top surface of the article which has cooling and does not continue to shrink resulting in a curved panel. It is desirable to provide a controlled cooling system for cooling of both the top and bottom surface of the formed article during continuous vacuum forming.